The present invention relates to a method of treating sewage and a sewage treatment system.
The disposal of human and animal waste is a large problem facing the world community, particularly in locations where population densities are high. In some cases, it is common practice, or at least known, to pump untreated or primary treated sewage into natural waterways or, for coastal cities, the adjacent ocean. Clearly this is an undesirable and unsustainable long-term solution.
In those locations that utilize secondary and tertiary treatment plants for processing the sewage, there are ongoing issues of cost and efficiency. These plants are large in area, are expensive to run, take considerable time to process the sewage, and consume large amounts of energy. Moreover, the improvement or expansion of such plants to cater for growth in populations is extremely capital intensive and can usually only be countenanced by taking a long term approach to seeing a financial return on that capital.
With the increased reluctance to invest more capital in expansion of the treatment plants, those plants are usually run at or near capacity. This increases the risk of accidental releases of raw or partially treated sewage into the waterways downstream of the plant. That, in turn, increases the risk of health concerns for those using those waterways and for the general health of the waterway itself. For example, raw or partially treated sewage is thought to contribute to algae blooms and other undesirable effects in river systems. In other cases, untreated or partially treated sewage is thought to contribute to increased rates of illness amongst beach goers.
Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
It is an object of the present invention, at least in a preferred embodiment, to overcome or substantially ameliorate one or more of the disadvantages of the prior art or at least provide a useful alternative.
According to a first exemplary embodiment of the present invention, there is provided a method for treating sewage in a fluid, the method including the steps of:
locating the sewage and the fluid in a holding tank;
releasing live fish into the holding tank; and
allowing the fish to consume and otherwise process the sewage whereby a layer of sediment is formed in the tank including waste from the fish.
Preferably, the method includes the step of progressively providing the fluid containing sewage to the tank. More preferably, the method includes the step of providing the fluid containing sewage to the tank at a predetermined rate. In some embodiments, the predetermined rate varies with time.
In a preferred form, the tank includes an overflow path and the method includes the step of continuing to progressively provide the fluid containing the sewage into the tank so that fluid and/or sewage progresses along the overflow path. More preferably, the holding tank is linked to a further tank and the method includes the step of allowing the fluid and/or sewage that progresses along the overflow path to flow into the father tank. Even more preferably, the method includes the step of releasing live fish into the further tank.
Preferably, the method includes the further step of removing the fluid from the tank. More preferably, the fluid is removed progressively over time. Even more preferably the fluid is removed by evaporation.
Alternatively, the fluid is removed once sufficient sewage has been processed by the fish. More preferably, the fluid is removed with any unprocessed sewage.
In a preferred form, the method includes the step of removing the layer of sediment from the tank.
Preferably, sewage and fluid are located in a plurality of tanks containing respective fish, and wherein after a predetermined period of fluid and any remaining sewage are removed from those tanks and placed in other tanks containing additional live fish.
Preferably also, the fluid is water. More preferably, the water is recovered from prior performances of the method described above.
According to a second embodiment of the present invention there is provided a sewage treatment system including a plurality of interlinked holding tanks for sequentially receiving sewage or sewage containing additional fluid and for containing live fish to consume and otherwise process the sewage whereby a layer of sediment is formed in the tank including waste from the fish.
According to a third embodiment of the present invention there is provided a method of producing fishmeal from sewage including the steps of:
introducing fluid into the sewage;
locating the sewage and the fluid in a holding tank;
releasing live fish into the tank; and
allowing the fish to consume and otherwise process the sewage whereby a layer of fishmeal is formed in a tank comprising waste from the fish and/or the fish themselves.
According to a fourth embodiment of the present invention there is provided a method for treating water containing sewage, the method including the steps of:
locating the water and sewage in a holding tank;
releasing live fish into the holding tank;
allowing the fish to consume and otherwise process the sewage whereby a layer of sediment is formed in the tank including waste from the fish;
removing the water from the tank.
According to a sixth embodiment of the present invention there is provided a method for producing fishmeal, the method including the steps of:
locating sewage and a fluid in a holding tank;
releasing live fish into the holding tank;
allowing the fish to consume and otherwise process the sewage whereby a layer of sediment is formed in the tank including waste from the fish; and
removing the fish from the tank and processing these to produce the fishmeal.
According to a seventh embodiment of the present invention there is provided a method for producing fishmeal, the method including the steps of:
locating sewage and a fluid in a holding tank;
releasing live fish into the holding tank;
allowing the fish to consume and otherwise process the sewage whereby a layer of sediment is formed in the tank including waste from the fish and the fish themselves;
removing the layer from the tank and processing this to produce the fishmeal.
Preferably, the processing includes adding grains to the fishmeal. More preferably, the grains are cereal grains such as wheat or barley.
According to an eighth embodiment of the present invention there is provided a method for treating sewage, the method including:
directing the sewage into a holding tank;
releasing live fish into the holding tank to consume and otherwise process the sewage; and
removing the fish from the tank.
Preferably, the fish are removed from the tank at a predetermined period after being released into the tank. However, in other embodiments, the fish are removed from the tank when they are of a predetermined size or weight. More preferably, the predetermined size or weight is based upon an average size or weight. In some embodiments the fish are released into the tank simultaneously and removed from the tank progressively.
Preferably, the fish are European carp and the predetermined period is about two months. More preferably, the predetermined period is about three months.
Preferably also, the holding tank includes a plurality of subdivisions through which the sewage is directed and the method includes the step of releasing live fish into each sub-division and subsequently harvesting the live fish from respective sub-divisions. More preferably, the method includes the step of sequentially releasing live fish into each sub-division More preferably, the method includes the step of harvesting the live fish from respective subdivisions in accordance with the sequence of the release of the fish.
In a preferred form, the method includes the step of progressively directing the sewage to the tank. More preferably, the method includes the step of directing the sewage into the tank at a predetermined rate. In some embodiments, the predetermined rate varies with time.
According to a ninth embodiment of the present invention there is provided a sewage treatment system including a plurality of interlinked holding tanks for receiving sewage and for containing live fish to consume and otherwise process the sewage.
According to a tenth embodiment of the present invention there is provided a method of producing fishmeal from sewage including the steps of:
directing the sewage into a holding tank;
releasing live fish into the tank; and
allowing the fish to consume and otherwise process the sewage;
removing the fish from the tank;
processing the fish to provide the fishmeal.
Preferably, the removing of the fish from the tank occurs at a predetermined period after their release into the tank. More preferably, the processing of the fish includes:
drying the fish to kill pathogens;
segmenting the fish to form pieces of fish;
combining the pieces of fish with additives to form a paste or powder; and
extruding the paste to form pellets of fishmeal.
Preferably also, the moisture content of the paste is about 10% to 15%. More preferably, the moisture content of the paste is about 11% to 13%. More preferably, prior to the extruding, the moisture content is varied by addition of water to the paste or powder or, alternatively, by drying the paste or powder.
In a preferred form, the pieces of fish are less than or about 1 cm3. However, in other embodiments, the pieces of fish are a different size and, more preferably, smaller.
Preferably, the combining of the pieces of fish with the additives includes agitating the pieces of fish both to encourage intermingling of the pieces with the additives and to further break down the pieces into smaller pieces.
Preferably also, the additives are chosen in response to the end use of the fishmeal.
According to an eleventh aspect of the present invention there is provided a method for treating water containing sewage, the method including:
locating the water and sewage in a holding tank;
releasing live fish into the holding tank;
allowing the fish to consume and otherwise process the sewage; and
removing the water from the tank
The term xe2x80x9csewagexe2x80x9d is intended in this specification and claims to include animal and/or human waste that is of one or more of a solid, semi solid and liquid form. Depending upon the context, that term also includes the water and/or other fluid that has been added to the waste to facilitate its passage through a sewer system. In some embodiments, additional water or fluid is added to the sewage while, in other embodiments, that is not required. For example, in the treatment of human waste, there is usually sufficient fluid, in the form of water, already part of the sewage. That water is added at the source of the sewage to facilitate the progression of the sewage through the sewer system and to the relevant treatment site. For animal waste, such as that generated in piggeries, it is often necessary to add additional fluid, usually water, to assist in the processing provided by the present invention.